Roasted coffee contains substances which cause coffee beverages to be intolerable to the digestive systems of many people. These undesired stimulants are mostly substances emanating from the coffee wax (Cf. U. Harms et al., KTM, Volume 19 (1969), Issue 6, pages 6 to 9 and Issue 7, pages 6 to 9). A portion of these substances enter into the coffee beverages during the normal manner of infusion.
The tolerability of the coffee beverage can thus be considerably improved by removal of the constituents of raw coffee beans which contribute to the presence of undesired stimulants. Carbonic acid-5-hydroxy-tryptamide (C-5-HT) can be considered as the indicator for the removal of these components (Cf. J. Wurziger, "Carbonic acid-5-hydroxy-tryptamide for the evaluation of fresh and treated coffee". 5th ASIC-Colloquium, Lisbon 1971).
The reduction of removal of these constituents is supposedly possible by means of different processes. According to the "Lendrich process" (Cf. German Patent No. 576,515) water steam under pressure and, according to the process of German Published Patent Application No. 16 92 284, liquid carbon dioxide act upon the raw coffee beans. However, constituents of the raw coffee bean which contribute to the presence of undesired stimulants in the roasted coffee remain substantially unaffected by these two processes.
Furthermore, it is known to treat raw coffee beans, which have not been treated with water, with a hydrocarbon halide at an elevated temperature (Cf. German Published Patent Applications Nos. 19 60 694 and 20 31 830). While these processes effectively remove constituents which contribute to the presence of undesired stimulants normally produced during roasting, the hydrocarbon halides used must be removed as completely as possible for health reasons. A modification of this process is described in Swiss Patent No. 568,719. In this case, a caffeine-containing hydrocarbon chloride is used as solvent. The reason for this is probably the fact that the raw coffee beans are preferably subjected to soaking with water or water steam before treatment with the solvent. By adding caffeine to the hydrocarbon chloride, reduction of the caffeine content of the raw coffee beans is to be prevented.
It is also known to treat raw coffee beans with an acetic acid ester in order to remove the constituents contributing to the presence of undesired stimulants normally produced during roasting. In this context, Published German Patent Application No. 20 31 830 mentions acetic acid ethyl ester and Swiss Patent No. 568,719 acetic acid isopropyl ester, while German Published Patent Application No. 26 18 545 mentions esters with a boiling point between 50.degree. and 100.degree. C. which are present in freshly roasted coffee in amounts greater than 10 ppm. While constituents of raw coffee beans contributing to the presence of undesired stimulants normally produced during roasting are actually extracted with the use of these solvents, the infusion of roasted coffee made of raw coffee beans treated in this manner invariably has an undesirable aftertaste which cannot be eliminated even by intensive removal of solvent residues from the treated raw coffee beans. This aftertaste is distinct enough to be identified by laymen in a blind test.
The removal from raw coffee beans of constituents which contribute to the presence of undesired stimulants normally produced during roasting has already been attempted by treating the raw coffee beans with such ketones having boiling points between 50.degree. and 100.degree. C. as naturally occur in freshly roasted coffee in amounts in excess of 10 ppm (Cf. German Published Patent Application No. 26 18 545). However, raw coffee beans treated according to this process always show light spots on the surface of the beans when roasted.